Final answer:
Based on the narrative provided, the answer to the question 'He was portly and low-backed and could not travel more than fifty miles in a day. I was often forced to whip him' is option 'C. Ox' as the text refers to a team of unbroken oxen'.
Step-by-step explanation:
The passage describes a situation where the subject is 'portly and low-backed and could not travel more than fifty miles in a day', and was 'often forced to whip him.' This suggests a beast of burden commonly used for work and transportation.
From the options provided, and considering the narrative style and context clues from the excerpts provided, the correct answer to this question appears to be C. Ox. The narrative mentions 'a team of unbroken oxen' and driving the oxen to collect wood. Additionally, it describes the physical struggle to manage the oxen, which aligns with the characteristics mentioned in the original question.